Propylene carbonate (4-methyl-1,3-dioxolane-2-one) is a colorless, aprotic solvent with a relatively high dielectric constant. It is widely used as a solvent for various synthetic polymers and as a reaction medium. Propylene carbonate is chiefly used as a non-aqueous solvent for electrolytes for high-energy batteries.
As a dielectric, propylene carbonate is generally suited for use in electrostatic apparatus. High energy or power densities can be attained in electrostatic apparatus when high electric fields are maintained at small injection or leakage currents within the dielectric used. The electric conductivity of commercial propylene carbonate which lies normally between 10.sup.-6 and 10.sup.-7 S/cm is however too high and thus not in a position to reduce leakage currents to a considerable extent. As a consequence, it cannot be used in an unpurified or only coarsely purified state.
The major impurities found in commercial propylene carbonate are propylene oxide, carbon dioxide, 1,2- and 1,3-propanediol (propylene glycol), allyl alcohol, ethylene carbonate, sodium ions, reaction products of tetramethyl ammonium bromide, water and other unidentified substances. The methods employed for determining these impurities, e.g. GC, IC or MS, are very troublesome.